Next summer I'm thinking about installing 2" Rigid Blue Foam to the bottom of of my trailer either above or below the underbelly sheathing to avoid having to skirt the trailer each fall. I move around each year, so re-skirting is required.

I'm wondering if anyone has tried to avoid skirting by attaching additional 2" rigid insulation to the bottom of the trailer. Has anyone tried this & was it effective?

Not sure which model you have, but on our rig, there is less than 1/2" of space between the coroplast and the lowest part of the gray and black tanks, if you were thinking of putting it above the coroplast. I'm not thinking you will get the most of the insulation adding it to the bottom of the rig, but you will be able to create a warmer space by doing the foam as a skirting around the rig, where you can safely place a couple electric heaters. There is quite a bit of floor area outside of the belly area, that is, the bottom of the slides and the area outside the frame that would be difficult to insulate from underneath, and only two inches of foam isn't a great deal of R value when you get down below freezing. Good luck.